Heretofore, it is known a sensor having attached thereto a detection element (sensor element) in the form of an axially extending plate and formed with a detection section at a front end side to face an object to be measured. Enumerated as such a sensor are a gas sensor such as a λ (lambda) sensor, a wide-range air/fuel ratio sensor, oxygen sensor and NOx sensor, and a temperature sensor for detection of temperature.
The plate-shaped detection element is generally configured so as to have a detection section at an axial (longitudinal) front end side and an electrode terminal section at a rear end side. There is a sensor that is regarded as one having such a detection element and that is configured to electrically connect a lead frame (metallic terminal member) made of an electrically conductive material to an electrode terminal section for thereby forming a portion of an electric current path for conduction of electrical current between the detection element and an external device. In the meantime, electrical currents such as detection current (detection signal) according to a result of detection by the detection element and electrical current for power supply to a heater in case the detection element has the heater are enumerated for conduction through the electrical current path electrically connecting the detection element and the external device.
As a sensor having a lead frame is known a sensor configured to use a lead frame having a resilient contact portion that serves as a resiliently deformable (deformable by a compressive force) leaf spring and hold a detection element within an insertion hole of a separator and in a state where an electrode terminal section of the detection element is brought into contact with the resilient contact portion of the lead frame (refer to Patent Document 1).
In case of a sensor with such a structure, it becomes possible to make good the contact condition of the lead frame and the electrode terminal section of the detection element by using a lead frame configured so that a resilient contact portion exerts a large resilient force. In the meantime, as a lead frame with a resilient contact portion exerting a large resilient force are enumerated, for example, a lead frame formed so as to be large in the width size, a lead frame formed so as to be large in the thickness, etc.
Patent Document 1: Unexamined Japanese Patent Publication No. 2001-188060 (FIG. 1, FIG. 6).
However, in case the resilient contact portion of the lead frame exerts an excessively large resilient force, a large pressure more than needed is applied from the lead frame to the detection element at the time of assembly of the lead frame and the detection element, so that a damage of the detection element such as chipping or breakage may possibly be caused by that pressure.
Further, in the event a lead frame (metallic terminal member) having a large width size is used as in the above-described prior art sensor, it is necessitated a wide space for disposition of the lead frame, so that there arises a problem that such a lead frame is not suited for use in a sensor that is needed to be small-sized. Further, in the event a lead frame large in the width size is used for a detection element formed with a plurality of electrode terminal sections that are small in the width size and positioned close to each other, one lead frame is brought into contact with all the plurality of electrode terminal sections, so that there is caused a possibility that a suitable electrical current path cannot be formed.
Over against such a problem, it will do to use a lead frame formed narrow in width and small in thickness. By using such a lead frame, it becomes possible to prevent the lead frame from applying an excessively large pressure to the detection element and make smaller the space for disposition of the lead frame. Further, by using a lead frame that is small in the width size, it becomes possible to prevent one lead frame from extending over a plurality of electrode terminal sections and contacting them.
However, a lead frame that is formed small in the width size or small in the thickness has a tendency to decrease in the rigidity.
In case under a condition where such a lead frame that is low in the rigidity is disposed in an element insertion hole of a separator, the detection element is inserted into the element insertion hole, the lead frame is liable to buckle due to the resistance to insertion at that time and be formed into an inadequate shape. When such deformation of the lead frame itself is caused, there arises a problem that suitable electrical connection between the lead frame and the electrode terminal section of the detection element cannot be attained or lead frames are brought into contact with each other to cause shortage.
Further, in case a sensor having a lead frame that is low in rigidity is, for example, subjected to a certain external force in actual use and its external shape is deformed, an inadequate external force is applied to the lead frame under the influence of the deformation of the sensor, thus possibly causing such a case where the relative positions of the lead frame and the detection element are changed. Namely, since the lead frame that is low in rigidity is liable to be deformed by an external force applied thereto, there is a possibility of the electrical connection between the lead frame and the electrode terminal section being unable to be maintained suitable when the lead frame is subjected to an inadequate external force to change the relative positions of the lead frame and the detection element.